Method of generating a curved blade retention slot in a turbine disk

ABSTRACT

A method of forming a curved slot in a turbine disk includes the steps of forming a pre-slot in the turbine disk and finishing the pre-slot to form a slot that receives a portion of a turbine blade. The turbine disk including a first face, an opposing second face, and an outer perimeter surface extending between the first face and the opposing second face. The pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face. An intersection between the outer perimeter surface and each of the first curved wall and the second curved wall is defined by a curved line.

BACKGROUND OF THE INVENTION

This application relates to a method of generating a curved bladeretention slot in a turbine disk of a gas turbine engine.

Gas turbine engines generally include turbine rotors having a pluralityof removable turbine blades and a plurality of associated static vanes.The turbine blades are mounted on a turbine disk.

FIGS. 1A and 1B show a front view and a side view, respectively, of arelated art turbine disk 46 including a plurality of straight slots 48for mounting turbine blades to a turbine disk 46. The turbine disk 46includes a first face 53, an opposing second face 55, and an outerperimeter surface 51 that extends between the first face 53 and theopposing second face 55. The straight slots 48 are generally fabricatedusing a broaching process. A broaching tool makes a pass through theturbine disk 46 to form an initial pre-slot passage in the turbine disk46. After forming the straight slots 48, an opening 59 of the straightslots 48 on the outer perimeter surface 51 of the turbine disk 46 isdefined by two substantially parallel lines 49. Additional broachingtools pass through the passage, enlarging the passage and defining theprofile of each of the straight slots 48. A drawback to the broachingprocess is that it can only form straight slots.

There is a need in the art for a method of generating a curved bladeretention slot in a turbine disk of a gas turbine engine that overcomesthe drawbacks and shortcomings of the related art.

SUMMARY OF THE INVENTION

A method of forming a curved slot in a turbine disk includes the stepsof forming a pre-slot in the turbine disk and finishing the pre-slot toform a slot that receives a portion of a turbine blade. The turbine diskincluding a first face, an opposing second face, and an outer perimetersurface extending between the first face and the opposing second face.The pre-slot includes a first curved wall and a second curved wall thateach extend between the first face and the opposing second face. Anintersection between the outer perimeter surface and each of the firstcurved wall and the second curved wall is defined by a curved line.

In another exemplary embodiment, a method of forming a turbine diskincludes the steps of forming a pre-slot in the turbine disk andfinishing the pre-slot to form a slot that receives a base of a turbineblade. The turbine disk includes a first face, an opposing second face,and an outer perimeter surface extends between the first face and theopposing second face. The pre-slot includes a first curved wall and asecond curved wall that each extend between the first face and theopposing second face. An intersection between the outer perimetersurface and each of the first curved wall and the second curved wall isdefined by a curved line. The method further includes the step ofinserting the base of the turbine blade into the slot of the turbinedisk, and a shape of the slot corresponds to a shape of the base of theturbine blade.

In another exemplary embodiment, a turbine disk includes a body portionincluding a first face, an opposing second face, and an outer perimeterextending between the first face and the opposing second face. A slot inthe body portion extends between the first face and the opposing secondface to receive a portion of a turbine blade. The slot defines anopening on the outer perimeter surface, and the opening is defined bytwo curved lines.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a front view of a related turbine disk including aplurality of straight slots;

FIG. 1B illustrates a side view of the related turbine disk including aplurality of straight slots;

FIG. 2 illustrates a simplified cross-sectional view of a standard gasturbine engine;

FIG. 3 illustrates a perspective view of a turbine blade;

FIG. 4A illustrates a front view of a turbine disk including a pluralityof curved slots;

FIG. 4B illustrates a side view of the turbine disk including aplurality of curved slots;

FIG. 5 illustrates a front view of the turbine disk with a cup-typeforming tool positioned to form a curved pre-slot;

FIG. 6 illustrates a side view of the turbine disk with the cup-typeforming tool positioned to form the curved pre-slot;

FIG. 7 illustrates a side view of the turbine disk including curvedpre-slots;

FIG. 8 illustrates a bottom view of the cup-type forming tool;

FIG. 9 illustrates several different cup-type forming tools;

FIG. 10 illustrates a front view of the turbine disk showing the curvedpre-slot;

FIG. 11 illustrates a step portion added to the cup-type forming tool;

FIG. 12 illustrates a front view of the turbine disk showing themachining of the shape of the curved slots;

FIG. 13 illustrates a side view of the turbine disk showing themachining of the shape of the curved slots;

FIG. 14 illustrates the machining of one side of the curved slot; and

FIG. 15 illustrates the simultaneous machining of both sides of thecurved slot.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 2, a gas turbine engine 10, such as a turbofan gasturbine engine, is circumferentially disposed about an engine centerline(or axial centerline axis 12). The gas turbine engine 10 includes a fan14, compressors 16 and 17, a combustion section 18 and turbines 20 and21. This application extends to engines without a fan, and with more orfewer sections. As is well known in the art, air is compressed in thecompressors 16 and 17, mixed with fuel and burned in the combustionsection 18, and expanded in turbines 20 and 21. The turbines 20 and 21include rotors 22 which rotate in response to the expansion, driving thecompressors 16 and 17 and the fan 14. The turbines 20 and 21 includealternating rows of metal rotating airfoils or turbine blades 24 andstatic airfoils or vanes 26. FIG. 2 is schematic, and the turbine blades24 and the vanes 26 are removable from the rotors 22. It should beunderstood that this view is included simply to provide a basicunderstanding of the sections in a gas turbine engine 10 and not tolimit the invention. This invention extends to all types of gas turbineengines for all types of applications.

FIG. 3 shows a turbine blade 24. A platform 42 is provided at a radiallyinner portion of the turbine blade 24, while an airfoil 40 extendsradially (as seen from the axial centerline axis 12) outwardly from theplatform 42. A curved base 44 located under the platform 42 has anirregular surface including fingers 25 and grooves 23.

FIGS. 4A and 4B show a front view and a side view, respectively, of anexemplary turbine disk 50. The turbine disk 50 includes a first face 84,an opposing second face 86, and an outer perimeter surface 94 thatextends between the first face 84 and the opposing second face 86. Aplurality of curved blade retention slots 52 extend from the first face84 and the opposing second face 86 of the turbine disk 50. An opening 98of the curved slots 52 on the outer perimeter surface 94 of the turbinedisk 50 is defined by two substantially curved lines 90. Curved walls 96that extend from the first face 84 to the opposing second face 86 of theturbine disk 50 define the curved slots 52. In one example, the curvedlines 90 are each an arc or a portion of a circle.

Each of the plurality of curved slots 52 receives the curved base 44 ofone of the turbine blades 24. Each of the plurality of curved slots 52is formed by a two step process. In the first step, a curved pre-slot 56is formed. In the second step, the curved pre-slot 56 is finished toform the curved slot 52. The curved slot 52 includes a plurality offingers 78 and grooves 80 (as shown in FIG. 12) and has a profile thatmatches the profile of the curved base 44 of the turbine blade 24.

As shown in FIGS. 5 and 6, in a first step, a cup-type forming tool 54forms the pre-slot 56 in the turbine disk 50 (as shown in FIG. 7). Thefirst step defines the location of the curved slots 52 and forms thegeneral shape. As shown in FIG. 8, the cup-type forming tool 54 has agenerally circular shape and a circumferential portion 58 having athickness Z. The circumferential portion 58 has an inner diameter Y andan outer diameter X defined from a central axis W of the cup-typeforming tool 54. The cup-type forming tool 54 may include a grindingwheel, a plated cubic boron nitride (CBN) wheel, a vitrified cubic boronnitride wheel, an inserted milling cutter or the like. As shown in FIG.9, the pre-slot 56 can be formed by a variety of different shapedcup-type forming tools 54A, 54B and 54C each having a differentthickness Z.

The cup-type forming tool 54 is positioned at a desired locationrelative to the turbine disk 50. An end surface 62 of thecircumferential portion 58, which defines a substantially circular ring,contacts a periphery 64 of the outer perimeter surface 94 of the turbinedisk 50 and rotates about the central axis W of the cup-type formingtool 54. The cup-type forming tool 54 is then moved radially inwardtowards a central axis 66 of the turbine disk 50 to form a u-shapedpre-slot 56 (shown in FIG. 10) that includes substantially arcuateshaped opposing walls. The arcuate shaped pre-slot 56 extends betweenthe faces 84 and 86 of the turbine disk 50 (as shown in FIG. 7). Theshape of the pre-slot 56 corresponds to the shape of the portion of thecircular circumferential portion 58 of the cup-type forming tool 54 thatforms the pre-slot 56. After the pre-slot 56 formed, the cup-typeforming tool 54 is removed from the pre-slot 56.

Next, the turbine disk 50 and/or the cup-type forming tool 54 is movedrelative to the other to position the cup-type forming tool 54 at adesired location relative to the turbine disk 50. Another pre-slot 56can then formed in the turbine disk 50. The location of the cup-typeforming tool 54 relative to the turbine disk 50 determines theorientation of the curved pre-slots 56 on the turbine disk 50. Thediameters X and Y of the cup-type forming tool 54 determine thecurvature of the pre-slots 56.

As shown in FIG. 11, in another example, a step portion 68 is positionedon the circumferential portion 58 to add additional contours to thecurved pre-slot 56. In one example, the step portion 68 includes a firstportion 70, a second portion 72 and a third portion 74. The firstportion 70 has a diameter greater than the second portion 72, and thesecond portion 72 has a diameter greater than the third portion 74.

In a second step, as shown in FIG. 12, the curved pre-slot 56 isfinished with a profiled finger type finishing tool 76 to form thecurved slots 52. That is, the second step defines the profile of thecurved slot 52. The profiled finger type finishing tool 76 may include aplated CBN tool, a vitrified CBN tool, a profiled end mill cutter or thelike. As shown in FIG. 13, the finger type finishing tool 76 moves alongthe curved pre-slot 56 in the path shown in the dashed line to form thefinal shape of the curved slots 52 that includes the plurality offingers 78 and the grooves 80. The profiled finger type finishing tool76 provides the pre-slot 56 with a shape that corresponds to the shapeof the curved base 44 of the turbine blade 24. Alternately, multipletools can be used to achieve the final shape of the slot profile.

In one example shown in FIG. 14, the profile machining can be achievedby machining one side of the curved pre-slot 56 at a time.Alternatively, as shown in FIG. 15, the profile machining can beachieved by simultaneously machining both sides of the curved pre-slot56 at the same time.

After machining, the curved slots 52 of the turbine disk 50 have thesame shape and curvature as the curved base 44 of the turbine blade 24.When the turbine blade 24 is to be installed in the turbine disk 50, thecurved base 44 of the turbine blade 24 is aligned with the curved slots52. The fingers 25 of the turbine blade 24 align with the grooves 80 ofthe curved slot 52, and the grooves 23 of the turbine blade 24 alignwith the fingers 78 of the curved slot 52. The turbine blade 24 is thenslid relative to the turbine disk 50 to install the turbine blade 24 inthe curved slot 52 of the turbine disk 50.

Compared to straight pre-slots of the related prior art, the exemplarycurved slots 52 facilitate reducing the stresses on the blade attachmentand the curved slots 52, facilitating increasing the retentioncapability of the turbine blade 24 in the turbine disk 50, andfacilitating reducing the size, weight and cost of the gas turbineengine 10.

The foregoing description is only exemplary of the principles of theinvention. Many modifications and variations are possible in light ofthe above teachings. It is, therefore, to be understood that within thescope of the appended claims, the invention may be practiced otherwisethan using the example embodiments which have been specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

What is claimed is:
 1. A method of forming a slot in a turbine disk, themethod comprising the steps of: forming a pre-slot in a turbine disk,the turbine disk including a first face, an opposing second face, and anouter circumferential surface extending between the first face and theopposing second face, and the pre-slot includes a first curved wall anda second curved wall that each extend between the first face and theopposing second face, wherein the step of forming the pre-slot includesrotating a forming tool about a central axis of the forming tool, thenmoving the forming tool to contact an outer circumferential surface ofthe turbine disk, and then moving the forming tool in a first directionradially inwards from the outer circumferential surface of the turbinedisk and towards a central axis of rotation of the turbine disk to formthe pre-slot, and then moving the forming tool radially outward from thepre-slot in a second direction towards the outer circumferential surfaceof the turbine disk and away from the central axis of rotation of theturbine disk and the pre-slot to remove the forming tool from thepre-slot, wherein the second direction is opposite to the firstdirection; and then finishing the pre-slot after the step of forming thepre-slot to form a slot that receives a portion of a turbine blade. 2.The method as recited in claim 1 wherein the step of finishing thepre-slot includes positioning a finishing tool in the pre-slot andforming at least one groove and at least one finger in the pre-slot toform the slot.
 3. The method as recited in claim 1 wherein twosubstantially curved lines define an opening of the slot on the outercircumferential surface of the turbine disk.
 4. The method as recited inclaim 1 wherein the pre-slot includes a bottom wall, and the firstcurved wall and the second curved wall are located on opposing sides ofthe bottom wall, and an entirety of first curved wall and an entirety ofthe second curved wall are substantially perpendicular to the bottomwall.
 5. The method as recited in claim 1 wherein a distance between thefirst curved wall and the second curved wall defines a width of thepre-slot, and the width is constant for an entire length of the pre-slotand along an entire height of the pre-slot.
 6. The method as recited inclaim 1 wherein an intersection between the outer circumferentialsurface with each of the first curved wall and the second curved wall isdefined by a curved line.
 7. The method as recited in claim 1 wherein atip of the forming tool includes two portions each having a differentdiameter.
 8. A method of forming a turbine disk, the method comprisingthe steps of: forming a pre-slot in a turbine disk, the turbine diskincluding a first face, an opposing second face, and an outercircumferential surface extending between the first face and theopposing second face, and the pre-slot includes a first curved wall anda second curved wall that each extend between the first face and theopposing second face, wherein a distance between the first curved walland the second curved wall defines a width of the pre-slot, and athickness is constant for an entire length of the pre-slot and along anentire height of the pre-slot, and an intersection between the outercircumferential surface and each of the first curved wall and the secondcurved wall is defined by a curved line, wherein the step of forming thepre-slot includes rotating a forming tool about a central axis of theforming tool, then moving the forming tool contact an outercircumferential surface of the turbine disk, and then moving the formingtool in a first direction radially inwards from the outercircumferential surface of the turbine disk towards a central axis ofrotation of the turbine disk to form the pre-slot, and then moving theforming tool radially outward from the pre-slot in a second directiontowards the outer circumferential surface of the turbine disk and awayfrom the central axis of rotation of the turbine disk and the pre-slotto remove the forming tool from the pre-slot, wherein the seconddirection is opposite to the first direction; then finishing thepre-slot after the step of forming the pre-slot to form a slot thatreceives a base of a turbine blade; and inserting the base of theturbine blade into the slot of the turbine disk, wherein a shape of theslot corresponds to a shape of the base of the turbine blade.
 9. Themethod as recited in claim 8 wherein the step of finishing the pre-slotincludes positioning a finishing tool in the pre-slot and forming atleast one groove and at least one finger in the pre-slot to form theslot.
 10. The method as recited in claim 8 wherein the pre-slot includesa bottom wall, and the first curved wall and the second curved wall arelocated on opposing sides of the bottom wall, and an entirety of firstcurved wall and an entirety of the second curved wall are substantiallyperpendicular to the bottom wall.
 11. The method as recited in claim 8wherein a distance between the first curved wall and the second curvedwall defines a width of the pre-slot, and the width is constant for anentire length of the pre-slot and along an entire height of thepre-slot.
 12. The method as recited in claim 8 wherein an intersectionbetween the outer circumferential surface with each of the first curvedwall and the second curved wall is defined by a curved line.
 13. Themethod as recited in claim 8 wherein a tip of the forming tool includestwo portions each having a different diameter.
 14. A method of forming aslot in a turbine disk, the method comprising the steps of: forming apre-slot in a turbine disk, the turbine disk including a first face, anopposing second face, and an outer circumferential surface extendingbetween the first face and the opposing second face, and the pre-slotincludes a first curved wall and a second curved wall that each extendbetween the first face and the opposing second face, wherein the step offorming the pre-slot includes positioning a forming tool relative to theouter circumferential surface of the turbine disk, rotating the formingtool about a central axis of the forming tool, the moving the formingtool to contact the outer circumferential surface of the turbine diskand then radially inwards towards a central axis of the turbine disk toform the pre-slot, and then moving the forming tool radially outwardaway from the pre-slot to remove the forming tool from the pre-slotwherein the forming tool is a cup having a wall defined by an innercircumferential surface and an outer circumferential surface, and thecup rotates about a central axis to remove a portion of the turbine diskwith the wall to define the pre-slot having the shape of the wall and acurvature of the inner circumferential surface and the outercircumferential surface; and then finishing the pre-slot after the stepof forming the pre-slot to form a slot that receives a portion of aturbine blade.
 15. The method as recited in claim 14 wherein, during thestep of forming the pre-slot when the cup is rotating about the centralaxis, a portion of the cup is located in the pre-slot and a reminder ofthe cup is located outside the pre-slot.
 16. The method as recited inclaim 14 wherein a direction of movement of the cup and the central axisof the cup is perpendicular to the central axis of rotation of theturbine disk.
 17. The method as recited in claim 14 wherein the wall ofthe cup that contacts the turbine blade is spaced away from the centralaxis of the cup.
 18. A method of forming a turbine disk, the methodcomprising the steps of: forming a pre-slot in a turbine disk, theturbine disk including a first face, an opposing second face, and anouter circumferential surface extending between the first face and theopposing second face, and the pre-slot includes a first curved wall anda second curved wall that each extend between the first face and theopposing second face, wherein a distance between the first curved walland the second curved wall defines a width of the pre-slot, and athickness is constant for an entire length of the pre-slot and along anentire height of the pre-slot, and an intersection between the outercircumferential surface and each of the first curved wall and the secondcurved wall is defined by a curved line, wherein the step of forming thepre-slot includes positioning a forming tool relative to an outercircumferential surface of a turbine disk, rotating the forming toolabout a central axis of the forming tool, then moving the forming toolto contact the outer circumferential surface of the turbine disk andthen radially inwards towards a central axis of the turbine disk to formthe pre-slot, and then moving the forming tool radially outward awayfrom the pre-slot to remove the forming tool from the pre-slot, whereinthe forming tool is a cup having a wall defined by an innercircumferential surface and an outer circumferential surface, and thecup rotates about a central axis to remove a portion of the turbine diskwith the wall to define the pre-slot having the shape of the wall and acurvature of the inner circumferential surface and the outercircumferential surface; then finishing the pre-slot after the step offorming the pre-slot to form a slot that receives a base of a turbineblade; and inserting the base of the turbine blade into the slot of theturbine disk, wherein a shape of the slot corresponds to a shape of thebase of the turbine blade.
 19. The method as recited in claim 18wherein, during the step of forming the pre-slot when the cup isrotating about the central axis, a portion of the cup is located in thepre-slot and a reminder of the cup is located outside the pre-slot. 20.The method as recited in claim 18 wherein a direction of movement of thecup and the central axis of the cup is perpendicular to the central axisof the turbine disk.
 21. The method as recited in claim 18 wherein thewall of the cup that contacts the turbine blade is spaced away from thecentral axis of the cup.